Installing a biomass boiler: what it's really like

We’re off the mains gas grid so I chose biomass (wood chip) to replace our old oil-fired boiler as I wanted to be as CO2 neutral as possible. It also meant there was no possibility of a catastrophic heating-oil spill. Our old, cold house already had central heating with radiators and we were told by the suppliers (Covers Eco-Centre in Chichester) that air- or ground-source heat pumps would require the installation of underfloor heating which wasn’t practical.

Covers made a site visit and recommended the Windhager BioWIN Exclusiv system. They also recommended a local installer who visited us to check the Covers suggestions. Before finalising the order, Covers made a second site visit with a Windhager technician.

At the end of all this, we’d decided to site the boiler inside an open-fronted car barn and run the water underground into the house. The heating matrix would sit in the place of the old boiler in our boot-room and connect onto our existing heating system. We would also run water to an outbuilding that I was converting into an office and which would have underfloor heating.

Installing all the Windhager kit went very smoothly but I then realised that, despite the numerous site visits, nobody had thought of how to move the water from the boiler into the house and out again to the outbuilding. It turned out that the initial order (and quote) had covered all the Windhager components but nothing else.

In the end, we decided to go for super-insulated underground pipes which added almost £2,000 to the cost of the system. We also had to dig holes through the house foundations and up inside with another through the floor of the car barn and then make good all the damaged floors etc.

Once the plumbing was complete and the mains electricity spurs laid in, Windhager themselves came to commission the system. They were super efficient and got everything running in a morning but I felt they could have spent a bit longer explaining how the system worked.

In order to minimise pellet use, the Windhager computer measures the outside air temperature and sets the water temperature accordingly so the radiators get hotter as the air outside gets colder. The indoor controller units do have temperature sensors as well but this is only used to moderate the circulating water temperature - they don’t function like the old-style on/off thermostats that I was used to.

I spent many a happy hour setting all the dials with a screwdriver before we had a house that wasn’t too hot on mild days and too cold on frosty mornings. I’ve got this all sorted now and we have a warm house for the first time since we moved in (although we do have a fine new Morso log-burning stove as well).

We are now very happy with the boiler but it’s much more of a lifestyle commitment than a gas or oil one. For a start, it’s huge. The boiler itself is twice as tall as our old oil-fired one and has a pellet hopper by the side which is as big again.

Then you have to factor in the pellets themselves. These are supplied in 10kg bags with a ton on a pallet costing just over £200 so each bag is a little over £2. On a really cold day, the boiler is on 24 hours and burns about 7 bags of pellets - it’s only 2 bags on a mild day. This means topping up the hopper anything between 2 and 5 times per week.

Filling the hopper generates a lot of dust which you wouldn’t want indoors and a pile of empty plastic sacks which I have yet to find a use for. In order to have some pellets in stock and take a delivery of new ones, you need room for at least 2 pallets. That’s as much space as a Mini. With 2 tons of pellets and the boiler in it’s protective box, it’s a single garage full of stuff. You also need a pallet truck to move the pellets (and that doesn’t work if they’re on the wrong kind of pallet) and at least two strong people to move them around. Add in lifting the 10kg bags to shoulder height to tip them into the hopper and you can cancel that gym membership.

Putting this little lot inside a house (as was initially suggested to me) is crazy. As it is, the water-distribution matrix looks like part of an aircraft carrier with its temperature gauges and brass taps. There are wires everywhere on it with thermostats and electrically operated valves all controlled by a central brain. It’s all rather lovely in a techno way but it’s not very homely and we’ve boxed ours in behind a false wall with access panels. That part of the system is also really noisy. It ticks and gurgles constantly and you certainly wouldn’t want to be watching TV or sleeping anywhere near it.

Don’t get me wrong, now it’s all installed I love it. We’ve got a warm house and we’re not burning fossil fuel. Delivering the pellets is no worse than delivering the heating oil and they’re made fairly locally in Andover. I like the physical connection to our energy usage although that may become more problematic as I get older.

I do think the system is more suited to light industrial units or groups of houses, though. Then you could have a massive hopper installed to take a year’s worth of pellets which can be delivered in bulk.

If you’re thinking of having one installed into an existing property, make sure that the installers give you a quote for absolutely everything you need and then factor in any extras for digging and refilling trenches, building storage buildings and hiring strong friends. You’re not just getting a heating system, you’re getting a whole new way of life. More like getting a dog, really.

I have installed a 40kW logboiler in an outbuilding 11m away from my house and am about to dig the trench connecting the boiler house and house (by hand if it will ever stop raining!). The trench will contain the flow and return from a heat-exchanger in the boiler house together with the 10mm.sq armoured mains cable and cold water. You mentioned your connections had been overlooked. I can't afford the £2000 you mentioned and had thought of using 28mm copper in armaflex insulation. Can you tell me what options you had for this part of the work and what you had to do where it entered the house. I am loathe to cut through the dp membrane in the floor. Updindor seemed expensive and I am not sure it is suitable for the temperature

One factual question: will your boiler only burn pellets or can it, as you say in the first paragraph, burn chips as well? Most boiler that burn chips can burn pellets - but not necessarily the other way round as the feed mechanisms are different and a chip boiler has to be able to handle variability in the fuel supply.

Do you have a buffer store with your system? If not, can you literally turn the boiler off and have it auto-relight on a timer/programmer which would permit its hopper full of fuel to last much longer?

One thing that makes a HUGE difference if your boiler isn't in the house is to super insulate the pipework in the unheated spaces. When I fitted that loft insulation in a plastic sleeve round the pipework in the boiler room, the boiler room got cold - which meant I was losing much less heat where I didn't need it!

Pellets come in 2 sorts of bags that I've seen: clear polythene and LDPE. The latter are the same material as used for supermarket bags, so you can certainly put the offcuts (from when you open the bags) into a supermarket recycling box. But you're right, what to do with the large stack of bags - I have enquired locally and there doesn't seem to be anyone recycling them in for what for a company is quite a small volume.

I think we will investigate the bulk tank this summer. It sounds like a good idea but it will need to hold at least 5 tons of pellets so it'll be too big to go inside the garage. Hopefully, it will fit onto the old heating oil tank base. Not sure of the cost but I'm sure it won't be cheap.

Agreed about adjusting the house temperature but I don't think it's as simple as tweaking the electronic controls as the whole thing is temperature compensated. As you suggest, the bulk tank would solve all these problems.

Glad you like the article. There is a frost protection setting which would reduce the amount of pellets used but I think the boiler would actually run 24/7 if it remained below freezing all day and night. You could go away for weeks if it was only frosty for a few hours each night but, as you say, you'd need a strong neighbour if you were away during a cold snap.

Running and plumbing in two boilers sounds like a nightmare to me and you'd still have to store the oil with all the attendant pollution risks. I think I'd be more inclined to use some kind of additional electric heating as a back up for if the pellets run out in the biomass boiler while you're away.

This is all really helpful - great to get real examples. I'm considering biomass, because it seems the easiest to retrofit in place of an oil boiler to work with existing central heating. My concern is about how long you can leave a biomass boiler unattended i.e. what if you want to go away for a month in the Winter and leave the heating on low/frost control setting? Your comment about being able bodied enough to lug the 10kg bags around, means a willing neighbour who would check your house for you if away in the Winter may also need to be fit enough to lug the bags around. I wondered if you'd considered this aspect - it's been suggested to me that you could keep oil boiler for use in such circumstances - but that's means having enough space for both and the hassle of maintaining 2 boilers. I'm in middle of Yorks Dales by the way so colder than where you are I think.